Nature-based solutions - Sustainable water management

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Constructed Wetlands for olive mill

Wastewater generated by olive mills need to be treated when is neither possible the discharge in sewer nor the field application. In these cases, constructed wetlands are starting to be considered as a nature-based option for olive mill wastewater treatment.


  • suitable for small/medium mills without sufficient land for fertigation
  • simple operation and maintenance
  • no odour issues
  • possibility to discharge in water bodies
  • possibility to avoid the installation of accumulation tanks, treating the olive mill wastewater also in oil production season
  • possibility to recover the concentrate

More information


Constructed wetland for olive mill

Several experiences on the use of constructed wetland (CW) for olive mill treatment are from Greece. Heroyvim et al. (2011), Michailides et al. (2015) and Tatoulis et al. 2016 tested the combination of trickling filters and tertiary treatment with constructed wetlands (vertical flow, free water surface, horizontal flow plus electro-oxidation). Grafias et al (2010) studied the combination of electro-oxidation with vertical flow systems. Stabilization pond as primary treatment and CW for further treatment stages were investigated by Gikas et al., 2013. Finally,  Kapellakis et al. (2012) have studied the option of free water systems fed with olive mill wastewater diluted at a ratio of 1:10. Greek experiences have shown high removal efficiencies: organic load 54-94%, TKN 44-98%, SS 52-83%, and phenols 60-95% (Masi et al., 2017).

Another option is to adopt total evaporative systems, without discharge of wastewater.

Recent innovative options are the use of evaporator-condenser plus constructed wetland. This combination was tested by Alfa Laval, azienda leader firm in the field of evaporative systems, together with the University of Florence and IRIDRIA S.r.l., in charge of wetland systems. The most important results of these tests were (Masi et al., 2014):

  • optimal treatability of the condensate with nature-based solutions, up to the water quality standards for discharge in water bodies according to Italian law
  • no need of accumulation tank to feed the evaporator

potential reuse of the concentrate as organic-rich amendment

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live mill wastewater (left), concentrate (centre) and condensate effluent from the evaporator-condenser plus CW tested by IRIDRA in collaboration with the University of Florence for the olive mill Santa Tea Reggello (FI, Italy)



IRIDRA's authors are highlighted in bold.

Masi, F., Rizzo, A. and Bresciani, R., Vayenas, D., Akratos, C., Tekerlekopoulou, A. and Stefanakis, A.I.,  Olive Mill Wastewater Treatment in Constructed Wetlands, in "Constructed Wetlands for Industrial Wastewater Treatment", Stefanakis A. (Ed.), Wiley, 165-135; 978-1-119-26834-5, 2018.

Masi, F., Bresciani, R., Munz, G., & Lubello, C. (2015). Evaporation–condensation of olive mill wastewater: Evaluation of condensate treatability through SBR and constructed Wetlands. Ecological Engineering, 80, 156-161.

Herouvim E, Akratos CS, Tekerlekopoulou A, Vayenas DV. Treatment of olive mill wastewater in pilot-scale vertical flow constructed wetlands. Ecological Engineering. 2011 Jun 30;37(6):931-9

Grafias P, Xekoukoulotakis NP, Mantzavinos D, Diamadopoulos E. Pilot treatment of olive pomace leachate by vertical-flow constructed wetland and electrochemical oxidation: an efficient hybrid process. Water Research. 2010 May 31;44(9):2773-80.

Gikas GD, Tsakmakis ID, Tsihrintzis VA, 2013. Treatment of olive mill wastewater in pilot-scale natural systems. Proc. of 8th Int. Con. of EWRA “Water Resources Management in an Interdisciplinary and Changing Context", Porto, Portugal, 26-29 June 2013, paper #232, pp. 1207-1216.

Kapellakis IE, Paranychianakis NV, Tsagarakis KP, Angelakis AN, 2012. Treatment of olive mill wastewater with constructed wetlands. Water 4:260-271.

Michailides, M., Tatoulis, T., Sultana, M-Y., Tekerlekopoulou, A.G., Konstantinou, I., Akratos, C.S., Vayenas, D.V., 2015. Start-up of a free water surface constructed wetland for treating olive mill wastewater. Hemijskaindustrija 69.

Tatoulis T., Stefanakis A., Frontistis Z., Akratos C.S., Tekerlekopoulou A.G., Mantzavinos D., Vayenas D.V. 2016. Treatment of table olive washing waters using trickling filters, constructed wetlands and electrooxidation, Environmental Science and Pollution Research, in press